In turbines, such as those and aircraft power plants, high operating efficiencies are generally associated with high operating temperatures. Internal temperatures of modern turbine engines may typically exceed 1500.degree. F., for example. Moreover, the increased efficiencies potentially obtainable at even higher temperatures have not been realized, largely because of limitations in the properties of materials in current use. Because of the deleterious effects of high temperature gases upon structural components, the use of a variety of metallic and nonmetallic materials have been considered, including the ceramics, tungsten alloys, and more recently, carbonized composites.
Carbonized composite materials are currently being employed in certain aerospace structures which sustain substantial mechanical and thermal stress. Typical applications include the leading edge portions of spacecraft which are exposed to high temperatures and stresses during reentry. Such composite materials typically include a fibrous component, for example, carbon or graphite fibers in a matrix of carbon derived from pyrolyzing a thermosetting polymer material, such as phenolic. Carbonaceous fibers such as polyacrylonitrile, rayon, and pitch based fibers are converted to carbon or graphite through pyrolysis techniques and are then impregnated with carbonaceous liquid materials. The impregnated fibers are available either in the form of interwoven cloth or roving or unidirectional "tape" in which bundles of the fibers are laid parallel to one another in a single direction without any cross-weave fibers interconnecting the fibers.
Processes for the manufacture of the composite materials typically entail the formation of an uncured workpiece substantially of the configuration desired for the structure. The workpiece is cured under a prescribed time/temperature/pressure cycle and then pyrolyzed to high temperatures to form a carbonized structure, having both fibrous and matrix components in the carbonized state. The workpiece is then densified in a multistep process to form a high strength carbonized structure. The carbonized workpiece, or substrate, may then be coated with an oxidation resistant coating typically containing silicon carbide and silicon metal. Such coated carbon-carbon materials have been demonstrated to maintain structural integrity when exposed to temperatures in excess of 2000.degree. F. and have substantially greater structural strength and toughness than most ceramic structures.
Although such carbon-carbon structures may be selectively reinforced to enhance resistance to stress loads along particular axes and at particular regions by appropriate orientation and configuration of the fibrous reinforcing material prior to cure, arrangement of such fibrous materials to withstand the high centrifugal forces encountered in a turbine engine rotor has not heretofore been achieved. Indeed, composite, carbon-carbon rotors used in turbine engines have been susceptible to disintegration from high centrifugal forces and high turbine temperatures. The possibility of the disintegration is increased where large rotor diameters are required and where higher speeds are likewise necessitated. A method of producing a composite ring suitable for incorporating in the rotor of a gas turbine engine is disclosed in U.S. Patent No. 3,966,523 to . Karl S. Jakobsen and David B. McLaughlin, issued June 9, 1976. The rotor disclosed in this patent incorporates a composite ring having a plurality of spirally wound filaments in adjacent relationship. This composite ring is manufactured by winding each filament into a polymer matrix to form a monolayer sheet having essentially circular filament hoops. The monolayer sheets are stacked in adjacent relationship and the polymer matrix is finally cured under pressure to form a unitized composite ring. In this design, little flexibility is provided for the design of various contours in producing the engine rotors, and further, the incorporation of the individual monolayer sheets as disclosed does not produce a rotor having an optimum rotational capability to withstand high speeds without failure for rotor blades of sufficient size to produce the greatest output.